After meeting my fiance, I gained a lot of weight, but I don't think it had anything to do with him since I had been gaining before I met him too.

I started losing when we moved in together actually, but we had already been dating for four years before we moved in together. I don't anticipate gaining when we get married because I am going to try to be a lifetime maintainer!
I think the main reason people say that newlyweds gain weight is that there is this theory that once you "got" your man, you aren't concerned with looking good anymore. I don't know if I buy that one. Some women gain weight planning a wedding b/c it is so stressful, and there is of course the honeymoon where you eat out a lot. I dunno. I think I ate the most with my BF when we were in college together, and also after he graduated I would visit him on the weekends, and him living in his bachelor pad, all he had to eat was rice and oatmeal, so we went out every meal!
Anyway, I guess what I am trying to say is that it is not uncommon for newlyweds to gain weight.